In a method of manufacturing a field effect type compound semiconductor device in the related art, a mesa isolating method of etching a semiconductor substrate is primarily used, and as a result, leakage current of a compound semiconductor device is increased and breakdown voltage is decreased due to occurrence electrical contact between a gate electrode and a channel layer of a mesa region. There occurs a problem that T gate metal is broken at a narrow opening portion of a gate pattern when a T gate electrode is formed by using an existing PMMA copolymer. In addition, when gate metal is evaporated to be thick in order to reduce resistance of the gate electrode, a T type resist pattern is deformed due to an increase in temperature of a vacuum evaporation apparatus, and as a result, it is difficult to form the T gate electrode stably and reproducibility of making a semiconductor device also deteriorates.
FIGS. 1A to 1D are vertical cross-sectional views of a device for each process to describe a making process and a structure of a semiconductor device having the T gate electrode in the related art and simply illustrates a method of manufacturing a field effect type compound semiconductor device such as indium-phosphorus (InP) high-electron mobility transistor (HEMT), a metal-semiconductor field effect transistor (MESFET), and the like.
First, as illustrated in FIG. 1A, a semi-insulating indium-phosphorus (InP) substrate 1, a InAlAs buffer layer 2, a InGaAs channel layer 3, an InAlAs spacer layer 4, an electron supply layer 5, a second InAlAs schottky layer 6, a second etching stop layer 7, a first InAlAs schottky layer 8, a first etching stop layer 9, are an N type InGaAs ohmic layer 10 are formed in sequence.
Subsequently, as illustrated in FIG. 1B, after a mesa region 11 is formed, an ohmic metal electrode 12 is formed as illustrated in FIG. 1C.
Next, as illustrated in FIG. 1D, after the T type resist pattern is formed by an electron ray exposure method by applying PMMA resist and copolymer resist, parts of an N type InGaAs ohmic layer 10 and a first AlAs etching stop layer 9 used to make a normally-on type semiconductor device are wet-etched and removed. Subsequently, in order to make the field effect type compound semiconductor device, when a first InAlAs Schottky layer 8 and a second etching stop layer 7 are etched, and PMMA resist and copolymer resist are removed by using a lift-off method after a gate metal constituted by Ti, Pt, and Au is evaporated, the field effect type compound semiconductor device having a T gate electrode 13 is made as illustrated in FIG. 1D. When the field effect type compound semiconductor device (HEMT) made by the above method is formed, electric contact occurs between the gate electrode and the channel layer of the mesa region due to mesa isolation, and as a result, the leakage current of the compound semiconductor device increases and the breakdown voltage decreases.
There occurs a problem that the T gate metal is broken at the narrow opening portion of the gate pattern when the T gate electrode is formed by using the PMMA copolymer and copolymer resist. In addition, when gate metal is evaporated to be thick in order to reduce the resistance of the gate electrode, the T type resist pattern is deformed due to the increase in temperature of the vacuum evaporation apparatus, and as a result, it is difficult to form the T gate electrode stably and reproducibility and reliability of making the semiconductor device deteriorate.